The present invention relates generally to an improved substrate for heat generating electronic and/or semiconductor devices and assemblies, and more particularly to an improved heat dissipating finned substrate for such devices and assemblies. The substrate comprises a metallic plate having a plurality of parallelly disposed fins projecting away from the surface and being weldably secured thereto. The substrate blank is formed, populated, and otherwise completed prior to final deployment of the fins so as to permit normal production techniques to be practiced, and without requiring special techniques and/or devices to avoid handling interference from the fins. In the course of the process of the present invention, an array of spaced parallelly disposed undeployed fin members are created on the heat dissipating surface of a rigid substrate, with the substrate blank thereafter being subjected to various assembly operations including the steps of treating the mounting surface and circuitry and also populating the substrate; all prior to deployment or extension of the fins. Accordingly, the substrate blanks of the present invention may be subjected to conventional assembly operations including that of treating the mounting surface and populating the substrate without requiring unusual steps or precautions to be taken to protect the configuration of outwardly extending metallic fins.
In order to enhance the thermal performance of substrate assemblies, metallic fins have typically been added to provide additional surface area for dissipation of thermal energy. The utilization of fins provides an additional mechanism for conducting heat away from the substrate member by providing substantially greater surface areas. However, in doing so, conventional assembly steps and/or operations are impeded or slowed whenever efforts are undertaken to perform work on a finned device, or alternatively to undertake to attach fins to an already-populated support. Because of the nature of the circuit packages or other components present on a populated circuitry surface, it is accepted that post-attachment of finned members is normally achieved by steps and/or operations which result in the finned members delivering poor thermal performance. For that reason, therefore, finned substrates have met with limited application in the industry.
In accordance with the present invention, an improved outwardly projecting finned heat dissipating substrate is created utilizing preformed fins in a nondeployed configuration, with these fins being weldably secured to the substrate plate or blank prior to deployment. The welded attachment provides enhanced thermally conductive properties for the final product. In addition, the structure of the present invention is arranged such that the fins remain undeployed and coplanar with the substrate until the steps of mounting of the circuit package, semiconductor devices, or other components onto the surface of the substrate is complete. Thereafter, and as a final or near final operation, the fins are deployed so as to be disposed substantially normal to the plane of the substrate. In other words, because of the novel techniques employed in securing or bonding the fin members to the substrate, the extended or deployed portions of the fins not only remain coplanar with the substrate during the fabrication and assembly operations, but the welded joint provides a highly thermally conductive bond. Since the actual deployment of the fins is undertaken as one of the final steps in the overall operation, assembly proceeds through the production using conventional operations unimpeded by the necessity of protecting or isolating the welded fins during the actual production/assembly steps.
In a typical procedure, a thin metallic sheet or foil is superimposed onto the metallic base surface of a substrate blank in order to create a preform assembly. Thereafter, the preform is interposed into a work station created between the energy delivery horn of an ultrasonic energy generator and a stable anvil, with the energy delivery horn being in surface-to-surface contact with the sheet or foil. An appropriate welding force is applied against the delivery horn while the ultrasonic generator is energized, with the preform being advanced through the work station at a work compatible with formation of continuous, uniform, and integral welded bands. The welding steps are repeated, as necessary, in order to create plural parallel spaced apart welded bands. It is frequently desirable to utilize multiple energy delivery horns in order to create multiple bands in a single pass, thereby reducing the number of repeat welding operations. Thereafter, the metallic sheet/foil is severed adjacent the same edge surface of each welded band to create unattached metallic sheet/foil spans between mutually adjacent welded bands. Either prior to or subsequent to the severing operation, the semiconductor or circuit package mounting surface is treated, undergoing such operations as creation or refinement of circuitry, device populating steps, and the like. Thereafter, and as a final or near-final operation, the foil spans are folded outwardly until they project normally to the plane of the substrate blank.
Therefore, it is a primary object of the present invention to prepare improved fin heat sinks, with the fins being weldably attached to the surface of the substrate/sink, and deployed to project outwardly as a final or near-final operation.
It is a further object of the present invention to provide an improved technique for the fabrication of finned heat sinks for semiconductor devices, wherein the sinks are provided with metallic fins projecting outwardly from the surface, and with the fins being weldably attached through ultrasonic welding techniques so as to achieve enhanced heat dissipating qualities and characteristics.